    <!doctype HTML PUBLIC "-//W3C//DTD HTML 4.01//en" "http://www.w3. org/TR/html4/strict.dtd">
    <head>
            <meta name="content-type" content="text/html; charset=utf-8">
            <title>圣诞树</title>
            <style>
                    #content{
                            height:680px;
                           
                    }
    /*树叶*/               
                    .tri{
                            width:0px;
                            height:0px;
                            border-style:solid;
                            border-width:50px;
                            border-top-width:0px;
                            border-color:green transparent;
                            margin:auto;
                    }
                    .tri1{
                            border-width:50px;
                            border-top-width:0px;
                    }
                    .tri2{
                            border-width:100px;
                            border-top-width:0px;
                    }               
                    .tri3{
                            border-width:150px;
                            border-top-width:0px;
                    }
    /*树干*/
                    #rectangle{
                            width:90px;
                            height:150px;
                            background:#CC9900;
                            margin:auto;
                    }
            </style>
    </head>
    <body>
            <div id="content">
                    <div class="tri tri1"></div>
                    <div class="tri tri2"></div>
                    <div class="tri tri3"></div>
                    <div id="rectangle"></div>
            </div>
    </body>